Process for the production of



7 used for example as bases.

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. -P fatented Oct 4,. 1960- PROCESS FOR THE PRODUCTION OF DLwuANiING-CAPRQLACTAM 2 Claims. (Cl. 260239.3).

The present invention concerns a new process for the: production of DL-a-amino-caprolactam, a valuable intermediate product for the production of lysine.

The stereoisomeric a-amino-caprolactams' can easily be hydrolysed to form the corresponding lysines, forexamplewith diluted hydrochloric acid. L(')-a-aminocaprolactam as well as DL-u-amino-caprolactam would therefore be excellently suitable as starting materials for the preparation of L(+)-lysine if they could be obtained in a simple manner and not just from the latter by latetamisation and, possibly, racemation; It has now surprisingly been foundthat DL-a-aminocaprolactam can be obtained in excellent yields if caprolactam is chosen as starting substance. This is treated first with phosphorus oxychloride, then with phosphorus pentachloride and finally with sulphuryl chloride; the

a.a-dichloro-caprolactim chloride is decomposed with water; and the a.a-dicbloro-capro1actam so obtained is reacted with catalytically activated'hydrogen in the presence of one mol of an inorganic or organic base, the DL-achloro-caprolactam. obtained is: reactedawithi a salt of hydrozoic acid-andzthe resultantDL-arazido-caprolactam is reacted with catalytically activatedrhydro gen.

In the first step, phosphorus oxychloride servesnot can be poured onto ice whereupon the a.oc-.dichlorocaprolactim chloride is immediately decomposed. In this way, a.u-dichloro-caprolactam is obtained in crude yields of 75-80% of the theoretical whereas J von Braun and A. Heymons, B. 63, 502, (1930) could only obtain yields of 30-40% of the theoretical when using phosphorus pentachloride as sole chlorinating agent in benzene.

The catalytic hydrogenation which follows in the second step can be performedfor example in the presence of Raney-nickel in methanol as solvent. Alkali hydroxides, alkali carbonates or tertiary organic bases can be With methanol as solvent, the use of triethaonlamine is particularly advantageous as the triethanolamine hydrochloride crystallises out during the hydrogenation in coarse granular form and so does not block the catalyst. It remains fully active therefore until the termination of the reaction. The triethanolamine hydrochloride can then easily be filtered off under suction and the base regained therefrom. The DL-u-chloro-caprolactam is obtained in yields of 85-90% of the theoretical. The compound was first obtained by H. Schechter and I. C. Kirk, J. Am. Chem. Soc. 73,

-309-1, 1951 inayieldof 31.4% by reactinghydrozoic acid with 2-chloro-cyclohexanone.

p In the third step, an-alkaliazide, in particular sodium azide, can be used for example as salt of hydrozoic acidand the reaction thereof with the DL-a-chloro-caprolactam: is performed in a neutral aqueous/alcoholic or 'aqueous/acetonic solution. On cooling the reaction solution, the DL-a-azido-caprolactam crystallises direct in good purity and in a yield of 80-85 of the theoreticah The compound hasnot-heretofore been described; it melts at 106-108".

Also the catalytic hydrogenation as the last reactionis' easy to:perform; for example Raney-nickel can be used as catalyst'and alcohol as solvent. If the hydrogenation is performed at normal pressure the nitrogen liberated can-- be removed by continually passing through hydrogen The development of nitrogen has-no influence onthe course of the reactionthe hydrogenation is performed under pressure; On distilling the crude hydrogenation product, the DL-u-amino-caprolactam is obtained in yields of 90-94% of the theoretical.

The following example further illustrates the method of performingthereaction according to the present invention. Parts are-given as parts by weight and theirrelationship to parts by volume is as grammes to cubic centimeters. The temperatures are in degrees centigrade.

parts (:275 parts by volume, 3 mols) of phosphorusoxychloride are cooled in a vessel fitted withastirrer,

thermometer, dropping funnel and a reflux condenser towhich a gas delivery, tube is attached, to aninner tem-- perature of 0. .226.3 parts (2 mols) of' pulverised, driedIcaprolactam are added: in-portions whilestirring duringwhich addition the temperature must never exceed 10. -After about30 minutes a clear solution has been obtained; To complete-the conversion of the acid amide. into thelactim chloride, 230' parts (l-.-l mols). of phosphoruspentachloride are added in portions to the solu- .tion which has been cooled to 2 to 5, during which addition the temperature again must not exceed 10.-

are added dropwise at first very slowly. and. carefully,

during which addition the temperature must remain be tween.0 and 15 and on completion of the dropwise addition,.the whole..-is.stirred. for another- 2 hours within the temperature range given. On then slowly heating. the

mixture a pale yellow, clear solution is obtained, at 25 sulphur dioxide and HCl gas begin to develop. -It is heated to 40 and stirred for 1 hour at this temperature, then some of the phosphorus oxychloride is distilled off by connecting the reaction mixture, heated to 35-40", to a water-jet vacuum for 90 minutes. The yellow oil which remains is poured in a thin stream on to 2.5 kg. of crushed ice, the ice being continuously stirred. The colourless crystallised u.u-dichloro-caprolactam is formed by decomposition of the lactim chloride. It is filtered ofi under suction, washed twice with water and dried in the vacuum at 50-60. Yield: 275 to 29l'parts, 80% of the theoretical.

The above product which still containsacid impurities is recrystallised from 280 parts by volume of methanol, sodium acetate being added to the hot, clear solution until the reaction is neutral. a.oc-Dichloro-caprolactam crystallises from the hot filtered solution when it is cooled to about 0. It is filtered off under suction and is washed twice with methanol, warmed to 5. Yield: 223-237 parts, 61-65% of the theoretical. M.P. 1245-1265 corrected. The mother liquor is evaporated to /3 of its volume and water is added at the boil under it remains cloudy. After cooling to about about '32 parts of yellowish product are obtained (9% of the theoretical). It'melts at 120-124 corrected. Total yield of recrystallised product having a neutral reaction: 7074% poured in with 50 parts by volume of methanol, are added tothis solution. Hydrogen is introduced at atmospheric pressure while shaking the solution. and a half hours, 11,50012,000 parts by volume of hydrogen have been taken up. At the same time triethanolamine hydrochloride crystallises out in the form of coarse granules. This hydrochloride and the catalyst are filtered ofi under suction and the filter residue is washed twice with methanol. The methanol in the filtrate is distilled off and the residue is dried in the vacuum at 95 The crystallising green residue is then dissolved in 150 parts by volume of. chloroform and the solution is shaken out with 150 parts by volume of 1 N-hydrochlon'c acid. The aqueous solution which has separated from the chloroform is shaken out twice with 50 parts by volume of chloroform each time. The combined chloroform extracts are dried with sodium sulphate, the chloroform is distilled off, the residue is dried in a Water jet vacuum at 95, recrystallised from 50 parts by volume of toluene, washed twice with 15 parts by volume of toluene each' time and dried in the vacuum. Yield: 49 parts of DL-a-chloro-caprolactam, 67% of the theoretical; M.P. 91-93. This product can be used .for the next step of the reaction. Its purityis due to the fact that it can be distilled in the vacuum Without residue and that a colourless distillate is obtained. After evaporation of the toluene mother liquor a crystallising oil remains. This consists of a mixture of diand 'mono-chloro-caprolactam in a ratio of about 1:2. In the next addition it is mixed with the a.u-dichloro-caprolactam. In this case, for the hydrogenation 85 parts of 0:,utdichloro-caprolactam, .18 parts of the residue of the mother liquor (containing about 6 parts of ma-dichlorocaprolactam) and 67.2 parts of triethanolamine are used. When recrystallised from toluene, 63 parts of DL-uchloro-caprolactam' (91% of the theoretical calculated on,

the starting product newly added) are obtained and, on evaporating the toluene mother liquor, again about 18 parts of the residue of the mother lye are obtained.

(0) Production of a-azido-caprolactam. 36.7 parts of u-chloro-caprolactam (0.25 mol), 19.5 parts of sodium azide (0.3 mol), 20 parts by volume of 95% alcohol and 50 parts ofwater are heated in a vessel fitted with a reflux condenser for 24 hours on a steam bath. On cooling, finally at about 0", the DL-u-azido-caprolactam crystal- Within one to one lises'out. It is filtered oit under suction and washed once with 15 parts by volume of 20% alcohol and twice with 15 parts of water each time. Yield: 30-325 parts, 78- of the theoretical, M.P. -108 corrected.

(d) Production of a-aminmcaprolactam. 1) At normal pressure: 60 parts by volume of 95% alcohol and 2 parts of Raney-nickel are placed in avessel fitted with a vibro-mixer, gas introduction and gas delivery tube. After the addition of 6.17 parts of a-azido-caprolactam (0.04

parts (05 mol) of a-azido-caprolactam are placed in an autoclave which can be shaken. The pressure is adjusted to 70 atmospheres hydrogen and then the autoclave is shaked for three hours at room temperature. The catalyst is then filtered ofi under suction, the solvent is distilled oh and the residue is distilled in the vacuum. DL-aamino-caprolactam is obtained which boils at 168172 under 13 mm. pressure at a bath temperature of Yield: 60 parts, 94% of the theoretical.

What we claim is:

l. DLa-az.ido-e-caprolactam.

2. In a process for the conversion of DL-oz-ChlOrO-ecaprolactam to DL-a-amino-e-caprolactam, the step of heating DL-a-chloro-E-caprolactam with an alkali metal azide in solution in a mixture of'water and a neutral water-miscible organic solvent, whereby the DL-a-azidoe-caprolactam, which is convertible by catalytic hydrogenation into the DL-a-amino-e-caprolactam, is produced.

References Cited in the tile of this patent UNITED STATES PATENTS 2,832,770 Hopkins et al n Apr. 29, 1958 2,876,218 Francis et a1. Mar. 3, 1959 V FOREIGN PATENTS 236,716 Switzerland July 16, 1945 OTHER REFERENCES Block: Chem. Reviews, vol. 38 (1946), pp. 548-9.

Theilheimer: Synthetic Methods of Org. Chem., vol 7, pp. 20; 192 (1953). a

Degering: Outline of Organic Nitrogen Compounds, p. 286 (1945 

2. IN A PROCESS FOR THE CONVERSION OF DL-A-CHLORO-ECAPROCACTAM TO DL-A-AMINO-E-CAPROLACTAM, THE STEP OF HEATING DL-A-CHLORO-E-CAPROLACTAM WITH AN ALKALI METAL AXIDE IN SOLUTION IN A MIXTURE OF WATER AND A NEUTRAL WATER-MISCIBLE ORGANIC SOLVENT, WHEREBY THE DL-A-AXIDO-A-CAPROLACTAM, WHICH IS CONVERTIBLE BY CATALYTIC HYDROGENATION INTO THE DL-A-AMINO-E-CAPROLACTAM, IS PRODUCED. 